Distributed Database Question Bank with Answers 06

Question:

Compare and analyze the relative merits of centralized and hierarchical deadlock detection approaches in a distributed DBMS.

Answer:

Centralized deadlock detection algorithms - Refer here.

A centralized deadlock detection scheme is a reasonable choice if the concurrent control algorithm is also centralized. It is better for distributed access patterns across sites since deadlocks occurring between any can be immediately identified. However, this benefit comes at the cost of communications between the central location and every other site. 

In hierarchical deadlock detection algorithms, sites are arranged hierarchically, and a site detects deadlocks involving only its descendant sites. To efficiently detect deadlocks, hierarchical algorithms exploit access patterns local to a cluster of sites. They tend to get the best of both worlds: they have no single point of failure (as centralized algorithms have), and a site is not bogged down by deadlock detection activities that it is not concerned with (as sometimes happens in distributed algorithms). For efficiency, most deadlocks should be localized to as few clusters as possible; the objective of hierarchical algorithms will be defeated if most deadlocks span several clusters.

A hierarchical deadlock detection scheme releases the burden of one single site for deadlock detection, and let more sites get involved. When access patterns are more localized, perhaps by geographic area, they may likely occur among certain sites with frequent communications. The hierarchical approach is more efficient in that it checks for deadlocks where they most likely happen, the hierarchical scheme splits deadlock detection efforts, thus resulting in greater efficiency.

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Question and answers on distributed deadlock detection approaches